Only unidirectional signal transmission can be performed in half-duplex transmission, and bidirectional signal transmission can be performed in full-duplex transmission. Therefore, signal transmission efficiency of the full-duplex transmission is extremely high. From a perspective of a physical layer, compared with the half-duplex transmission, a system throughput of the full-duplex transmission is doubled. The full-duplex transmission also has innovative impact on design of Media Access Control (MAC) such that a future wireless communications system can obtain a higher throughput.
Half-duplex transmission is mainly used in a current wireless communications system such as a WI-FI system or a Long Term Evolution (LTE) system. Signal sending and receiving cannot be simultaneously performed on a same time-frequency resource in the half-duplex transmission. In the other approaches, a full-duplex transmission method used in a WI-FI system is described, and signal sending and receiving can be simultaneously performed on a same channel in the WI-FI system. Because WI-FI transmission may occupy the entire channel, and does not need frequency multiplexing, resource allocation is fixed, and user equipment needs little time to prepare to transmit a signal. Therefore, after detecting or receiving some preambles, the WI-FI system can immediately transmit a signal in order to implement full-duplex transmission.
However, the foregoing full-duplex transmission solution is applicable to only the WI-FI system, and is inapplicable to an LTE system that needs frequency multiplexing, because resource allocation in the LTE system needs to be dynamically determined, and user equipment needs to perform rate matching according to a size of an obtained transport block. Compared with the WI-FI system, in the LTE system, the user equipment needs more time for resource configuration. In a frequency division duplex (FDD) mode in a current LTE system, for uplink scheduling, a base station sends uplink scheduling information to user equipment four milliseconds (ms) earlier, and for downlink scheduling, the user equipment needs to obtain in advance scheduling-related information from the base station, for example, a channel state indication (CSI), a cache size, and a scheduling resource. Downlink scheduling information and downlink data may be transmitted in a same subframe. A scheduling process in the FDD mode may be applied to the LTE system to implement full-duplex transmission. For example, n is a natural number. In an (n−4)th subframe, the base station sends uplink scheduling information for transmitting an uplink channel in an nth subframe, and the base station transmits downlink scheduling information in the nth subframe at the same time. In this way, the user equipment can simultaneously perform signal sending and receiving in the nth subframe.
In the described full-duplex transmission solution implemented in the LTE system, when sending the uplink scheduling information in the (n−4)th subframe, the base station is still unsure of whether there is also downlink transmission in the nth subframe for the same user equipment. In addition, there are different transmission power requirements for uplink transmission in the full-duplex transmission and that in the half-duplex transmission. As a result, the base station is unsure of whether there is a problem of self-interference cancellation in the uplink transmission in the nth subframe in the full-duplex transmission. Consequently, uplink channel power control in the nth subframe cannot be correctly set. Because imprecise power control results in intense self-interference, and the self-interference is hard to be canceled, downlink data is undetectable. Consequently, in the other approaches, in the full-duplex transmission implemented in the LTE system, a system gain is extremely low.